A power source element (power storage element) such as a battery cell and a capacitor within a power source apparatus generates heat during charge and discharge. A cooling apparatus (cooling mechanism) provided for the power source apparatus is used to cool the power source element to control the temperature of the whole power source apparatus, thereby achieving stabilization of the power source element, long life thereof, and stabilization of power supply.
Methods of cooling the power source apparatus (power source element) include gas cooling and liquid cooling. Heat from the power source element is transferred to a gas or liquid cooling medium, then transferred to a case which forms part of the power source apparatus, and dissipated to the outside of the power source apparatus. In the gas cooling, the cooling medium is easier to handle than that in the liquid cooling. However, the thermal conductivity of the cooling medium is lower than that in the liquid cooling. On the other hand, in the liquid cooling, the cooling medium is difficult to handle. For example, a sealing mechanism is required for preventing a leak of the cooling liquid from the power source apparatus. However, the liquid medium has a higher thermal conductivity than that of the gas medium to allow higher cooling efficiency.
In recent years, a power source apparatus such as a secondary battery and an electric double layer capacitor (condenser) is used as a battery of a hybrid car or an electric car. For saving space, a plurality of power source elements are placed at a high density to provide a higher power output. The liquid cooling with the high thermal conductivity is often employed in order to dissipate heat within the densely placed power source elements efficiently from the outer periphery thereof.
In a power source apparatus cooled through the liquid cooling, a cooling liquid is filled into a lower case which forms part of the power source apparatus, a plurality of power source elements are placed in the lower case filled with the cooling liquid, and an upper case (lid member) is put to seal the case containing the cooling liquid and a power source module formed of the plurality of power source elements. When the power source element generates heat due to charge/discharge, the generated heat is transferred to the cooling liquid, then to the case from the cooling liquid, and is finally dissipated to the outside of the power source apparatus. During the process, the cooling liquid is convected (naturally convected) within the sealed case in the same manner as gas. The action of the convection and the thermal conductivity of the cooling liquid itself cause the heat to be dissipated from the power source apparatus to the outside.
As described above, the thermal conductivity and the convection of the liquid are major contributors to the cooling efficiency in the liquid cooling. Patent Document 1 has proposed a technique to stir a coolant with a stirrer for the purpose of improving the cooling efficiency.
[Patent Document 1] Japanese Patent Laid-Open No. 6 (1994)-124733 (paragraph 0016, FIG. 3 and the like)